Ink-jet printing comprises ejecting ink droplets from orifices in a print head onto some type of receiving media to form a desired image. These printers generally use solid ink or phase change ink. Solid ink or phase change ink printers conventionally receive ink in a solid form, sometimes referred to as solid ink sticks. The solid ink sticks are typically inserted through an insertion opening of an ink loader for the printer, and are moved by a feed mechanism and/or gravity toward a heater plate. The heater plate melts the solid ink impinging on the plate into a liquid that is delivered to a printhead assembly for jetting onto a recording medium. The recording medium is typically paper or a liquid layer supported by an intermediate imaging member, such as a metal drum or belt.
A printhead assembly of a phase change ink printer typically includes one or more printheads each having a plurality of ink jets from which drops of melted solid ink are ejected towards the recording medium. The ink jets of a printhead receive the melted ink from an ink supply chamber, or manifold, in the printhead which, in turn, receives ink from a source, such as a melted ink reservoir or an ink cartridge. Each ink jet includes a channel having one end connected to the ink supply manifold. The other end of the ink channel has an orifice, or nozzle, for ejecting drops of ink. The nozzles of the ink jets may be formed in an aperture, or nozzle plate that has openings corresponding to the nozzles of the ink jets. During operation, drop ejecting signals activate actuators in the ink jets to expel drops of fluid from the ink jet nozzles onto the recording medium. By selectively activating the actuators of the ink jets to eject drops as the recording medium and/or printhead assembly are moved relative to each other, the deposited drops can be precisely patterned to form particular text and graphic images on the recording medium.
Proper operation of an inkjet requires the maintenance of a meniscus of ink at the jet orifice. As the ink cycles through a pulse sequence this meniscus may move slightly but a uniform response is required across all the jets to achieve reliable jetting and good directionality. The meniscus can be affected by nozzle contamination. Nozzle contamination may be caused by dust, paper fibers, ink, etc. that accumulates on the nozzle or face plate of a print head. Removing this contamination and air bubbles that may have entered the inkjet channels can be accomplished by purging ink usually by applying pressure to the ink such that it flows out of the orifice carrying the contaminant or air bubble. The ink may flow by gravity to the bottom of the face plate or be assisted by a wiping mechanism or vacuum. For successful printhead operation the face plate must able to shed the excess ink of purging or ink that otherwise accumulates around the jet aperture. Contamination around the jet aperture or deterioration of the surface quality near the jet aperture can lead to spontaneous loss of the ink meniscus often described as drooling.
Drooling, or the loss of the ink meniscus in the jet aperture, results in an unacceptable loss of print quality. Other than as described above, drooling may be caused by any combination of the inherent property of some ink formulation types, ink aging, sporadic contamination of ink, and/or mechanical degradation of the face plate coating. Both wear/damage ink adhesion or other issues lead to print head failure, and increases run costs.
As such, there is desired an alternative to the conventional print head face plate coatings that are used. In particular, a more robust coating is desired—one that is both resistant to surface damage and displays minimal surface wetting that leads to drooling or flooding of solid inks or ultraviolet (UV) curablecurable inks. Ideally, an ink jet front face coating should adhere well to the face plate surface, form a cohesive 1-5 micron coating across the surface, and display hydrophobic and/or oleophobic interactions when in contact with inks. The advantages of such a coating would be fewer print head related defects, and longer front face life.